(1) Field of the Invention
The present invention relates to a substrate contact electrode and a method of fabricating the same.
(2) Description of the Related Art
One of the previously known method of fabricating a contact electrode for a substrate includes a method using a tungsten bump which is made of refractory metal formed through a selective tungsten CVD (Chemical Vapor Deposition) method and etch-back of a polyimide applied film. FIGS. 1A-1F show schematic sectional views of a conventional structure for explaining the sequential steps for fabrication a tungsten bump on an MoSi.sub.2 /Al wiring by the above tungsten bump method.
Referring to FIGS. 1A-1F, firstly, an SiO.sub.2 film 5 is formed on an MoSi.sub.2 /Al wiring 15 by the CVD method, and a contact hole or through-hole 6 is formed in SiO.sub.2 film 5 (FIGS. 1A and 1B). Tungsten (W) 16 is selectively filled in the through-hole 6 by the tungsten selective CVD method (FIG. 1C) and, thereafter, the SiO.sub.2 film 5 on the MoSi.sub.2 /Al wiring 15 is etched away by the RIE (Reactive Ion Etching) method (FIG. 1D). Further, polyimide 4 is applied on the surface (FIG. 1E), and a part of the polyimide film 4 is etched back to provide a structure in which the bottom of a tungsten bump 17 formed on the MoSi.sub.2 /Al wiring 15 is embedded in the polyimide film 4 (FIG. 1F).
The above fabricating method has the following problems to be solved.
In the first place, in order to obtain a tall tungsten bump 17, tungsten 16 must be filled in a deep through-hole 6 by the tungsten selective CVD method as shown in FIG. 1C. However, in the filling of the tungsten, selectivity of tungsten deposition is lost so that tungsten 18 may be deposited on a part of the SiO.sub.2 film 5 as shown in FIG. 2A. As a result, in the subsequent etching for the SiO.sub.2 film 5, the tungsten deposited partly on the SiO.sub.2 film serves as a mask, and thus a part of the SiO.sub.2 film is left like a stick 19 as shown in FIG. 2B.
Secondly, in etching back a part of the polyimide applied film using oxygen plasma as shown in FIG. 1F, because of absence of an etching stopper, it is difficult to control the thickness of the film to be left. Further, in the oxygen plasma etching, a high resistance oxide film will be formed on the entire surface of the tungsten bump 17.
Thirdly, the tungsten formed by the tungsten selective CVD method is polycrystalline so that the mechanical strength of the resultant tungsten bump 17 is weak.
In the fourth place, where the tungsten bump 17 is formed according to the process steps of FIGS. 1A-1F on the semiconductor substrate having a convex portion 14 (shown in FIG. 3) on its surface, the substantial or effective height of the bump becomes low by the height of the convex portion.